Process heater



Oct. 4, 1966 Filed July 23, 1964 s. A. GUERRxERl 3,276,435

PROCESS HEATER C3 Sheecs-Sheet l Ail* INVENTOR. SALVATORE A. GUERR/ER/ATTORNEY OC- 4, 1965 s. A. GUERRxER 3,276,436

PROCESS HEATER Filed July 23. 1964 5 Sheets-Sheet :2

F'IG. 2

FLUX

RELAT/VE 0.5 c ,l z c DEGREES FROM PO//VT 48 ON TUBE 30 INVENTOR.SLVATORE A. GUERR/ER/ A T TOR/VEV Oct- 4, 1966 s. A. GUERRIERI 3,276,436

PROCESS HEATER Filed July 25, 1964 5 Sheets-Sheet 5 United States PatentO 3,276,436 PROCESS HEATER Salvatore A. Guerrieri, Rowayton, Conn.,assignor to The Luinmus Company, New York, NEI., a corporation ofDelaware Filed .Iuly 23, 1964, Ser. No. 384,707 12 Claims. (Cl. 122-356)This invention relates in general to a new and improved process heaterand reradiators therefore, and more particularly, to a process heaterutilizing tubes through which process fluid passes while being heatedwithin a chamber, the heater being capable of achieving more uniformheating around the tubes. Heaters according to the invention are furthercapable of increasing the heat iiux around the process Itubes withoutincreasing the maximum local heat flux or, conversely, providing thesame average flux to the tubes with a lower maximum local heat flux.

In process heaters, it is common practice to arrange the tubes in a linein the center of the furnace and to heat Athe tubes by burning fuelalong walls parallel to the tubes. This is done in order to satisfy, asnearly as possible, the design criteria of achieving uniform heat fluxaround the tube circumference. Despite this arrangement, the heat fluxaround a tube varies from a maximum along lines directly opposite thefiring walls to a minimum along lines ninety degrees therefrom. Thearrangement of the tubes in the center with the burning of fuel alongthe walls parallel to the tubes minimizes the difference in heat ux atdiametrically opposite spots on the tubes immediately opposite the amebecause these spots see essentially the radiant heat sources directly.On the other hand, this arrangement does not materially help the fluxvariation between a spot on the tube directly opposite the flame and aspot ninety degrees away from it.

Therefore, it is the general object of this invention to reduce theforegoing and other difficulties of prior art practices by the provisionof a new and improved process heater which is better in operation andless expensive to manufacture.

Another object of this invention is the provision of a new and betterprocess heater in which more uniform heat flux is achieved about thecircumference of the process tubes in the furnace chamber.

Still another object of this invention is the provision of a new andbetter process heater in which the process tubes have a higher averageheat liux thereabout with a lower total heat transfer surface, withoutthe necessity of increasing the temperature in the heater.

Other objects and advantages of the present invention will be made clearin the course of the following description of several embodimentsthereof, and the novel features will be particularly pointed out inconnection with the appended claims.

A better understanding of the invention will be gained by referring tothe following detailed description, in conjunction with the drawings,and wherein:

FIGURE l is a cross sectional elevation of a rectangular process heaterbuilt in accordance with the principles of the present invention;

FIGURE 2 is a partial horizontal cross sectional plan view of theprocess heater of FIGURE l, taken along lines 2-2 thereof;

FIGURE 3 is a curve of the heat flux computed about one quadrant of theprocess tube of FIGURE 2, with and without the reradiating surfaces ofthe present invention;

FIGURE 4 is a cross sectional elevation of an annular pyrolysis heaterbuilt in accordance with the principles of the present invention; and

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FIGURE 5 is a partial cross sectional plan view of the apparatus ofFIGURE 4.

In FIGURE l, there is shown a process heater built in accordance withthe principles of the present invention and generally designated by thenumeral 10. Process heater 10 is rectangular in shape, has a top wall12, a bottom wall 14, and side walls 16 and 18 which define arefractory-lined heating chamber 20. The side walls I6 and 1S haveburners 22 and 24 mounted therein and extending the length and widththereof. The purpose of having a plurality of burners is to enable sidewalls 16 and 18 to approach, as nearly as possible, a uniform radiatingplane. The burners 22 and 24 are supplied with fuel through conduits 26and 28, respectively, provided with suitable valves (not shown).

As shown in FIGURE 1, vertically extending process tubes 3ft are placedin the center of the chamber 20, equidistant from side walls 16 and I8.Process tubes 30 are supplied with a reactant mixture through an inletconduit 32. The inlet conduit 32 feeds a common manifold 34 whichsupplies the reactants to all of the tubes Si). The manifold 34 isconne-cted through a coupler 36 to the tube 30 with each of the tubeshaving their own individual coupler. After passing through the tube 30,the reaction products are removed through a manifold 38 which is coupledto the .tube 30 through a coupler 46. The manifold 38 is connected to anoutlet conduit 42.

It will be easily seen that the present invention can be utilized with avariety of types of process heaters, for example, such as a steamreformer or a pyrolysis heater. In some embodiments it may be desirableto have the tubes 3i) at one side or the other of chamber 2t), ratherthan centrally located as in FIGURE 1.

The tubes 30 and 31] are manufactured of a material suitable for theoperating conditions (i.e., reactants, furnace atmosphere, pressure,temperature, etc.). As shown in FIGURE 2, the tubes 30 and 3G are spacedone from another a distance of approximately two diameters from centerto center. Between adjacent tubes there is placed a vertically extendingrod 44 extending the length of the tubes 36 and .30 and in line with thecenters of the tubes 30 and 30. Rods 44 shall hereinafter be calledreradiators, and may be manufactured of any metal, alloy, ceramic, orcombination of such materials, which will give a high emissivity,strength and low cost. In the embodiment of FIGURE 2, the reradiator issquare in cross section with a thickness one quarter the tube diameter.Instead of square cross section, however, reradiators of rectangularcross section may be used, and they may be arranged with either theirwide or narrow sides facing the tubes. The range of useful sizes for thereradiator lies between about one eighth and one half of a tubediameter, any combination of these dimensions for width and thicknessand any orientation of the reradiators which may be desirable beinguseable for any given case.

The reradiators should be made of materials having an emissivity as nearunity as possible, or of materials coacting with a substance which willgive emissivity of near unity. The reradiators can 'be hollow in shape,but a solid reradiator will generally perform better, as it has `a lowertemperature gradient between the sides facing the radiator sources andthe sides facing the tubes. It is evident that since the reradiators arenot subjected to any internal or external pressures, they may be madeout of the lowest cost material available which is capable ofwithstanding the atmosphere and temperature within the chamber.

In operation, a reactant mixture such as, for example, a steam-methanemixture, is fed through process tubes 39 and subjected to the hightemperature (1400-2200 'F.) maintained within chamber 20 by burners 22,24. In the instance described, that of steam reforming, a nickel oxidecatalyst within the tubes 30 catalyzes the steam reforming reaction,resulting in the production of hydrogen together with some CO, CO2 andother reaction products. It will easily be understood that the points 48and 50 on the tube 30, which are closest to the radiating side walls 16and 18, are points of maximum heat linx. These points 48 and 50 areperpendicular to the common center line of the tubes 30 and 30. The sidewalls 16 and 18 provide radiant heat directly through the burners 22 and24, respectively, and additionally, reradiate heat rellected thereon sothat the points 48 and S0 nearest the side walls 16 and 18 receive themaximum heat flux.

In `FIGURE 3, the results of calculations of the heat flux about onequadrant of the tube 30 are shown from maximum point 48 closest toradiant Wall 16, to minimum point 52 ninety degrees from point 48. Thecalculations indicate the changes in relative radiant heat llux as afunction of the position on the periphery of the tube 30. The point 48is thus indicated as a 0 point and point 52 is the 90 point. In FIGURE3, curve AB has been provided to indicate the relative radiant heat lluxabout the tube 30 without the reradiators 44. Curve AB thus shows thatthe point 48 directly opposite the radiant walls 16 receives radiantheat at an equivalent rate equal to unity. Point 48 has been chosen as arelative point as it is known to receive the maximum heat flux. A pointon the tube 30 which is thirty degrees from the point 48 receivesradiant heat at a relative rate of only 0.92. Fortyfive degrees from themaximum point 48 there is a relative radiant heat flux of only 0.82.Sixty degrees from the maximum point 48 there is only a relative heatflux of 0.72. Finally, at ninety degree point 52 there is only 0.65relative heat flux.

A second curve AC, is shown in FIGURE 3, which shows the relative heatflux of the tube 30 with the reradiators 44 in place. A portion of curveAC is shown as a broken line 'because its position and shape has notbeen exactly calculated, but it is considered to lbe substantiallycorrect. It will be noted that the curve AC shows that with thereradiators 44 in place, the relative heat llux at the ninety degreeposition 52 is now 0.83. Even at a point seventy-tive degrees from themaximum point 48 of the tube 30, the relative heat flux is approximately0.80. Thus, the difference between the maximum heat flux and the minimumheat llux has been changed from 0.35 when the reradiators 44 are notutilized -to 0.17 when the reradiators 44 are in place. It shouldfurther be noted that in addition to the above advantage, the averageheat flux about the tube 30 has also been increased significantly by thereradiators 44. The average heat ux to the tube 30 without thereradiators 44 is approximately 0.82 in varbitrary units, whereas theaverage heat flux to the tube 30 with the reradiators 44 in place isapproximately 0.87. This represents an increase in capacity of at leasttive percent for the tube, making no allowance for the expectedimprove-ment due lto a more uniform wall temperature due to thereradiators 44.

It is to be observed that the use of the reradiators along the centerline of the tubes does not affect the radiant flux to any appreciableextent up to a position of approximately sixty degrees away from thereference point 48. It is only in the region of the ninety degreeposition that -a marked increase in heat flux is obained. This isespecially advantageous, as it is only about the ninety degree positionthat it is essential to increase the radiant heat flux so as to avoidthe great difference between the maximum and minimum radiant heat fluxabout the periphery of the tube.

It is obvious that reradiators having other shapes than those disclosedcan be utilized, and that the shape of the lreradiator would have aneifect on the redistribution of the radiant heat llux. For example,under certain conditions it may be desirable for reradiators 44 to haveconvex A' or concave surfaces facing either the tubes or the burners.All such configurations are to be included in the terms reradiatorselongated reradiators and rod-shaped reradiators, as deiined herein.

In FIGURE 4, there is shown the present invention as embodied in aprocess heater having an annular chamber. The pyrolysis heater 74 has acylindrical outer wall 76 with a refractory lining 78, and a cylindricalinner vwall with a refractory liner 82. The outer wall 76 and the innerwall 80 define, together with top and bottom walls, an annular chamber84 therebetween. The outer wall 76 is supported on suitable structuralsteel members 85. Centrally disposed within the inner wall 88 there is aconvection section 86 and a stack 88. Suitable ducts 90 provide apassage for combustion fumes from the annular chamber 84 into theconvection section 86 and stack 88. The operation of the annular furnace74 is more fully described in my copending patent application Ser. N-o.384,706, tiled July 23, 1964, and entitled Apparatus The inner wall 80has a plurality of burners 92 along the length and width thereof. Also,the outer wall 76 has outer wall burners 94 along the length and widththereof. The burners 92 and 94 are intended to heat vertically extendingprocess tubes 96 centrally disposed in a circular path within theannular chamber 84. The tubes 96 are spaced equidistant the inner wall80 and the `outer wall 76, but this is not a critical limitation. Asshown, the process tubes 96 may be used as a pyrolysis heater in theproduction of ethylene. The fuel for the process is supplied through aninput conduit 98 and removed through an outlet conduit 100. Thepyrolysis heater has reverse bends 102 for permitting a plurality ofpasses of the process fluid through the process tubes 96.

Between adjacent process tubes 96, there are positioned verticallyextending reradiating rods 104 extending the length of tubes 96. Therods 104 are similar to the rods 44 associated with the tubes .30 ofFIGURE 2. The rods 104 perform the same function described with respectto the rectangular furnace l0 in that they achieve a more uniform heatflux about the circumference of the process tubes 96 and also increasethe average heat ilux to the process tubes. The rods 104 are placedequidistant adjacent tubes 96 along the circular path of the centerlines of the tubes 96, which circular path is coaxial with the inner andouter walls 80 and 76 forming the annular chamber 84.

It will be understood that the embodiment of the invention set forthhereinabove are illustrative only and that various changes in the steps,materials and arrangements `of parts may be made by those skilled in theart Within the scope of the invention as defined in the appended claims.

I claim as my invention:

1. A process heater comprising:

a housing dening :a heater chamber therein;

means capable of heating said chamber;

said housing including two spaced radiating surfaces in said chamber;

a plurality of process tubes arranged in :a single row -in said chamberin spaced relation to `one another and to said radiating surfaces;

inlet means for supplying process liuid to said tubes and outlet meansfor removing said fluid after passing through said tubes in saidchamber; and

a plurality of rod-shaped reradiators equidistant be1 tween adjacenttubes and presenting heat absorbing surfaces to said heating means andreradiating sur- -faces to said tubes.

2. The process heater as claimed in claim 1, wherein said reradiatorsurfaces have -a high emissivity.

3. The process heater as claimed in claim 1 wherein said reradiators arerectangular in cross section `and have a width and lthickness betweenone eighth and one half of the tube diameter.

4. The process heater as claimed in claim 1, wherein said reradiator issolid throughout so as to provide a low temperature gradient and iscapable `of withstanding the temperature and atmosphere `of said heater.

5. The process heater as claimed in claim 1, wherein said radiatingsurfaces are planar.

6. The process heater as claimed in claim 1, wherein said radiatingsurfaces `are cylindrical, said cylindrical surfaces being coaxial toform an annular chamber, said tubes being arranged in a circular pathcoaxial with said surfaces, said reradiators being arranged in thecircular path of said tubes.

7. A process heater comprising:

a housing Vdening a heating chamber therein;

burner means in said chamber;

said housing including two spaced radiating surfaces in said chamberwith said burner means mounted therein;

a plurality of process t-ubes in said chamber between said radiatingsurfaces :and spaced in relation to one another, said process tubesbeing -in a single plane;

reradiators spaced between adjacent process tubes in said plane, saidreradiators having a high emissivity;

inlet means for supplying process fluid to said tubes;

and

'outlet means for removing said fluid after passing through said tubesin said chamber.

8. The process heater as claimed in claim 7, wherein said reradi-atorsextend the length of said tubes, said reradiators being smaller in`cross section than said tubes,

said reradiators being shaped to absorb heat from said burner means andreradiate heat toward the portions of said tubes closest to saidreradiators.

9. The process hea-ter as claimed in claim 8, wherein the `diameter ofeach `of said tubes is equal, said reradiators are rectangular in crosssection, and said reradiators have a width and thickness between oneeighth and one half of a tube diameter.

10. The process heater as -claimed in claim 9, wherein said reradiatorsare solid.

11. The process heater `as claimed in claim 9, wherein said reradiatorsare hollow.

12. In the construction of process heaters having process tubes disposedin a single row between heat-radiating surfaces, the improvement whichcomprises elongated reradiators disposed equidistant between :adjacenttubes, said reradiators being shaped to absorb heat from saidheatradiating surfaces and reradiate 'heat towards the portion of saidtubes closest thereto.

References Cited by the Examiner UNITED STATES PATENTS 559,021 4/1896Baker 110-98 2,081,971 6/1937 Alther 122-356 2,274,256 2/ 1942 Praeger122-356 2,326,492 8/ 1943 Praeger 122-356 2,625,918 1/1953 Lumly 122-3562,638,879 5/1953 Hess 122-356 CHARLES I. MYHRE, Primary Examiner.

1. A PROCESS HEATER COMPRISING: A HOUSING DEFINING A HEATER CHAMBERTHEREIN; MEASN CAPABLE OF HEATING SAID CHAMBER; SAID HOUSING INCLUDINGTWO SPACED RADIATING SURFACES IN SAID CHAMBER; A PLURALITY OF PROCESSTUBES ARRANGED IN A SINGLE ROW IN A SAID CHAMBER IN SPACED RELATION TOONE ANOTHER AND TO SAID RADIATING SURFACES; INLET MEANS FOR SUPPLYINGPROCESS FLUID TO SAID TUBES AND OUTLET MEANS FOR REMOVING SAID FLUIDAFTER PASSING THROUGH SAID TUBES IN SAID CHAMBER; AND